Method and apparatus for transmitting and receiving different signal types in communication systems

ABSTRACT

A method and apparatus are provided for transmitting a Reference Signal (RS) by a User Equipment (UE) in a wireless communication system. The method includes transmitting a DeModulation Reference Signal (DM RS) and information data in a sub-frame; and transmitting a Sounding Reference Signal (SRS) in a last symbol in another sub-frame. The DM RS is transmitted in a middle symbol in each slot of the sub-frame, and the information data is transmitted in other symbols in each slot of the sub-frame.

PRIORITY

This application is a Continuation Application of U.S. application Ser.No. 13/413,274, which was filed in the U.S. Patent and Trademark Officeon Mar. 6, 2012, as a Continuation Application of U.S. application Ser.No. 12/182,556, which was filed on Jul. 30, 2008, now U.S. Pat. No.8,155,100, issued on Apr. 10, 2012, and claims priority to U.S.Provisional Application Nos. 60/962,584 and 60/974,305, which were filedin the U.S. Patent and Trademark Office on Jul. 30, 2007 and Sep. 21,2007, respectively, the content of each of which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed, in general, to wireless communicationsystems and, more specifically, to a Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) communication system.

2. Description of the Art

In particular, the present invention is directed to the transmission andmultiplexing of Reference Signals (RSs) in SC-FDMA communicationsystems.

Several types of signals should be supported for the properfunctionality of a communication system. In addition to data signals,which convey information content of a communication, control signalsalso need to be transmitted from User Equipments (UEs) to their servingBase Station (BS or Node B) in the UpLink (UL) of the communicationsystem and from the serving Node B to the UEs in the DownLink (DL) ofthe communication system in order to enable the proper transmission ofdata signals. For example, control signals include positive or negativeacknowledgement signals (ACK or NACK, respectively), transmitted by a UEin response to (correct or incorrect, respectively) data packetreception and Channel Quality Indication (CQI) signals conveyinginformation about the DL channel conditions experienced by the UE.Furthermore, RSs (also known as pilots) are typically transmitted byeach UE having UL data or control transmission. These RSs providecoherent demodulation for the transmitted data and will be referred toas DeModulation (DM) RSs.

The present invention considers the UL communication and assumes thatthe transmission of signals carrying the data content information fromUEs is through a Physical Uplink Shared CHannel (PUSCH) while, in theabsence of data information, the transmission of control signals fromthe UEs is through the Physical Uplink Control CHannel (PUCCH).

A UE, also commonly referred to as a terminal or a mobile station, maybe fixed or mobile and may be a wireless device, a cellular phone, apersonal computer device, a wireless modem card, etc. Additionally, aNode B is generally a fixed station and may also be called a BaseTransceiver System (BTS), an access point, etc.

The UEs are assumed to transmit data or control signals over aTransmission Time Interval (TTI), which in an exemplary embodiment ofthe present invention corresponds to a sub-frame.

FIG. 1 illustrates a block diagram of a sub-frame structure 110 assumedin an exemplary embodiment of the present invention for PUSCHtransmission. The sub-frame includes two slots. A first slot 120 furtherincludes seven symbols used for the transmission of data and/or controlsignals. Each symbol 130 further includes a Cyclic Prefix (CP) formitigating interference caused by channel propagation effects. Thesignal transmission in one slot may be in the same part or it may be ata different part of the operating bandwidth than the signal transmissionin the other slot. In addition to symbols carrying data or controlinformation, some symbols may be used for the RS transmission, i.e., DMRS 140, to provide channel estimation and enable coherent demodulationof the received signal. It is also possible for the TTI to include onlyone slot or more than one sub-frames.

The transmission BandWidth (BW) is assumed to include frequency resourceunits, which will be referred to herein as Resource Blocks (RBs). Anexemplary embodiment of the present invention assumes that each RBincludes 12 sub-carriers, and that UEs are allocated a multiple N ofconsecutive RBs 150 for PUSCH transmission and 1 RB for PUCCHtransmission. Nevertheless, it should be noted that the above values areonly illustrative and should restrict the described embodiments of theinvention.

In order for the Node B to determine the RBs where to schedule the PUSCHtransmission by a UE and the Modulation and Coding Scheme (MCS) used forthe data, a CQI estimate is needed over the PUSCH transmission BW, whichis smaller than or equal to the operating BW. Typically, this CQIestimate is obtained through the transmission by the UE of another RSsounding the scheduling bandwidth (Sounding RS or SRS). This SRS istransmitted in a symbol of an UL sub-frame replacing the data, it isused to provide a Signal-to-Interference and Noise Ratio (SINR) estimateover the RBs comprising its transmission BW, and it can be further usedfor UL Transmission Power Control (TPC) and UL synchronization.

FIG. 2 illustrates an exemplary embodiment for SRS transmissionoccurring in one sub-frame symbol every 2 sub-frames for a respective4.3% SRS overhead. UE1 210 and UE2 220 multiplex their PUSCHtransmissions in different parts of the operating BW during a firstsub-frame 240, while UE2 220 and UE3 230 multiplex their PUSCHtransmissions in different parts of the operating BW during a secondsub-frame 250. In some symbols of the sub-frame, the UEs transmit DM RSin order to enable the Node B receiver to perform coherent demodulationof the data signal transmitted in the remaining symbols of the sub-framewith UE1, UE2, and UE3 transmitting respectively DM RS 260, 270, and280.

In the exemplary structure illustrated in FIG. 2, the first symbol everysecond sub-frame is used for SRS transmission 290. The UEs having SRStransmission may or may not have PUSCH transmission in the samesub-frame. The SRS transmission may occupy a different part of theoperating BW than the data or DM RS transmission from a UE. Moreover,although in the exemplary embodiment the SRS transmission occurs duringthe first symbol of a sub-frame, any other symbol, such as the lastsymbol of a sub-frame, may be used.

An exemplary block diagram for data transmission through SC-FDMAsignaling is illustrated in FIG. 3. Referring to FIG. 3, the encodeddata 310 is provided to a Discrete Fourier Transform (DFT) unit 320, thesub-carriers 330 corresponding to the assigned transmission BW areselected 340, the Inverse Fast Fourier Transform (IFFT) is performed350, and finally the Cyclic Prefix (CP) 360 and filtering 370, such astime windowing, are applied to the transmitted signal. Zero padding isassumed to be inserted by the reference UE in sub-carriers used for thesignal transmission by another UE and in guard sub-carriers (not shown).

Moreover, for brevity, additional transmitter circuitry such asdigital-to-analog converters, analog filters, amplifiers, transmitterantennas, etc., are not illustrated in FIG. 3. Similarly, the encodingprocess and the modulation process for the data, which are well known inthe art, such as turbo coding and Quadrature Phase Shift Keying (QPSK),or Quadrature Amplitude Modulation (QAM) 16, or QAM64 modulation, arealso omitted for brevity.

FIG. 4 illustrates an exemplary transmitter structure for the DM RS,which is assumed to be based on the time-domain transmission of ConstantAmplitude Zero Auto-Correlation (CAZAC) sequences and will besubsequently described in detail.

In FIG. 4, a CAZAC-based sequence 410 is cyclically shifted 420. The DFTof the resulting sequence is obtained 430, the sub-carriers 440corresponding to the assigned transmission BW are selected 450, the IFFTis performed 460, and finally, the CP 470 and filtering 480 are appliedto the transmitted signal 490. Zero padding is assumed to be inserted bythe reference UE in sub-carriers used for the signal transmission byanother UE and in guard sub-carriers (not shown).

The exemplary transmitter structure illustrated in FIG. 4 can also beused, possibly with minor modifications (such as the repetition in timeof the CAZAC-based sequence to produce a comb spectrum), for the SRStransmission.

As for the data transmission, for brevity, additional transmittercircuitry such as digital-to-analog converters, analog filters,amplifiers, transmitter, etc., are not illustrated in FIG. 4.

An alternative generation method for the transmitted CAZAC-basedsequence, serving as DM RS or as SRS, is in the frequency domain. Thisis illustrated in FIG. 5. For the SRS it is also possible that theselected sub-carriers are not consecutive (comb spectrum) in order tomultiplex SRS transmissions from multiple UEs over different BWs.However, this is not material to the present invention.

Referring to FIG. 5, the generation of the transmitted CAZAC-basedsequence in the frequency domain follows the same steps as in the timedomain with two exceptions. The frequency domain version of theCAZAC-based sequence is used 510 (that is, the DFT of the CAZAC-basedsequence is pre-computed and not included in the transmission chain) andthe cyclic shift 550 is applied after the IFFT 540. The selection 520 ofthe sub-carriers 530 corresponding to the assigned transmissionbandwidth, and the application of CP 560 and filtering 570 to thetransmitted signal 580, as well as other conventional functionalities(not shown), are the same as previously described for FIG. 3.

At the receiver, the inverse (or complementary) transmitter functionsare performed. For the DM RS, this is conceptually illustrated in FIG.6, in which the reverse operations of those in FIG. 4 apply, and in FIG.7, in which the reverse operations of those in FIG. 5 apply.

Referring to FIG. 6, an antenna receives the Radio-Frequency (RF) analogsignal and after being processed by further processing units (such asfilters, amplifiers, frequency down-converters, and analog-to-digitalconverters) the digital received signal 610 passes through a timewindowing unit 620 and the CP is removed 630. Subsequently, the receiverunit applies an FFT 640, selects 650 the sub-carriers 655 used by thetransmitter, applies an Inverse DFT (IDFT) 660, removes the cyclic shift670 applied to the transmitted CAZAC-based sequence and, using a replicaof the CAZAC-based sequence 680, multiplies (correlates) with theresulting signal 690 to produce an output 695 that can be used forchannel estimation or CQI estimation for the UL channel.

Similarly in FIG. 7, the digital received signal 710 passes through atime windowing unit 720 and the CP is removed 730. Subsequently, thecyclic shift of the transmitted CAZAC-based sequence is restored 740, anFFT 750 is applied, the selection 760 of the transmitted sub-carriers765 is performed and correlation 770 with the CAZAC-based sequencereplica 780 is subsequently applied. Finally, the output 790 is obtainedwhich can then be passed to a channel estimation unit, such as atime-frequency interpolator, or a CQI estimation unit for the ULchannel.

As for the transmitter, functionalities that are well known in the art,such as channel estimation, demodulation, and decoding are not shown forbrevity, as they are not material to the present invention.

As mentioned above, the RS (DM RS or SRS) is assumed to be constructedfrom CAZAC-based sequences. An example of such sequences is given by thefollowing Equation (1):

$\begin{matrix}{{c_{k}(n)} = {{\exp\left\lbrack {\frac{j\; 2\pi\; k}{L}\left( {n + {n\frac{n + 1}{2}}} \right)} \right\rbrack}.}} & (1)\end{matrix}$

In Equation (1), L is a length of the CAZAC sequence, n is an index ofan element of the sequence n={0, 1, 2 . . . , L−1}, and k is an index ofthe sequence itself. For a given length L, there are L−1 distinctsequences, if L is prime. Therefore, an entire family of sequences isdefined as k ranges in {1, 2 . . . , L−1}. However, it should be notedthat the CAZAC sequences used for the CQI and RS generation need not begenerated using the exact above expression as will be further discussedbelow.

For CAZAC sequences of prime length L, the number of sequences is L−1.As the RBs are assumed to include an even number of sub-carriers, with 1RB including 12 sub-carriers, the sequences used to transmit theACK/NACK and RS can be generated, in the frequency or time domain, byeither truncating a longer prime length (such as length 13) CAZACsequence or by extending a shorter prime length (such as length 11)CAZAC sequence by repeating its first element(s) at the end (cyclicextension), although the resulting sequences do not specifically fulfillthe definition of a CAZAC sequence. Alternatively, CAZAC-based sequencescan be generated through a computer search for sequences satisfying theCAZAC properties.

Different cyclic shifts of the same CAZAC sequence provide orthogonalCAZAC sequences. Therefore, different cyclic shifts of the same CAZACsequence can be allocated to different UEs and achieve orthogonalmultiplexing of the RS transmitted by these UEs in the same RBs. Thisprinciple is illustrated in FIG. 8.

Referring to FIG. 8, in order for the multiple CAZAC-based sequences810, 830, 850, and 870 generated correspondingly from multiple cyclicshifts 820, 840, 860, and 880 of the same root CAZAC-based sequence tobe orthogonal, the cyclic shift value A 890 should exceed the channelpropagation delay spread D, including a time uncertainty error andfilter spillover effects. If T_(S) is the duration of one symbol, thenumber of cyclic shifts is equal to the mathematical floor of the ratioT_(S)/D. For 12 cyclic shifts and for symbol duration of about 66microseconds (14 symbols in a 1 millisecond sub-frame), the timeseparation of consecutive cyclic shifts is about 5.5 microseconds.Alternatively, to provide better protection against multipathpropagation, only 6 cyclic shifts should be used, providing timeseparation of about 11 microseconds.

The present invention assumes that the PUCCH transmission is entirelybased on CAZAC-based sequences and, similarly to FIG. 1 for the PUSCH,corresponding exemplary PUCCH structures for ACK/NACK transmission andCQI transmission are respectively illustrated in FIG. 9 and FIG. 10.Also as for PUSCH VoIP transmissions, the PUCCH transmission in thefirst slot of a sub-frame is assumed to occur at a different part of theoperating bandwidth than the PUCCH transmission in the second slot ofthe sub-frame.

In the exemplary structure illustrated in FIG. 9, a UE transmitsACK/NACK 910 in four symbols of each slot and RS 920 in three symbols ofeach slot. Both ACK/NACK and RS transmissions are based on thetransmission of a CAZAC-based sequence 930 (modulated in case ofACK/NACK by the respective ACK/NACK bits). The multiplexing of ACK/NACKsignals and RS from different UEs is through the use of different cyclicshifts of a CAZAC-based sequence, as previously described, and throughthe use of orthogonal covers {W1, W2, W3, W4} 940 of length 4, such asWalsh-Hadamard codes, for the ACK/NACK and length 3 {H1, H2, H3} 950,such as DFT codes, for the RS.

In the exemplary setup illustrated in FIG. 10, the CQI bits 1010 aretransmitted in five symbols of each slot and the respective RS 1020 istransmitted in two symbols of each slot. The multiplexing of CQI signalsand RS from different UEs is again through different cyclic shifts of aCAZAC-based sequence (modulated in case of CQI) 1030. An orthogonalcover {G1, G2} 1040 of length 2, such as Walsh-Hadamard, may also applyfor the RS transmission.

The transmitter and receiver structures for the CAZAC-based sequencesused in PUCCH transmissions are practically the same with thecorresponding ones in FIG. 4 and FIG. 5 (transmitter) and FIG. 6 andFIG. 7 (receiver), respectively, and are not repeated for brevity.

An exemplary embodiment of the present invention considers Voice overInternet Protocol (VoIP), which represents an important application incommunication systems. Unlike data packets, VoIP packets typicallyoccupy a predetermined BW of a few RBs due to their small size. For BWfragmentation reasons, due to the single carrier property, and forfrequency diversity of VoIP transmissions, the RBs may be towards oneedge of the operating BW in the first slot and towards the other edgeduring the second slot of the sub-frame. Also, unlike data packets, VoIPpackets are typically transmitted at predetermined time intervals, suchas once every 20 msec.

Given that a large number of VoIP UEs, such as 200-300 at 5 MHz systemBW or 400-600 at 10 MHz system BW, may be active for a fully loadedsystem, the respective SRS transmission overhead is an importantconsideration. For example, if 600 VoIP UEs for 10 MHz system BW areequally divided over a period of 20 msec and assuming a 50% voiceactivity factor, 15 VoIP UEs will be transmitting in every sub-frame. Inseveral operating environments the number of cyclic shifts that can beused to orthogonally multiplex CAZAC-based sequences transmitted overcommon BW is much smaller than 15 and substantial overhead is requiredto support SRS transmissions from VoIP UEs.

Therefore there is a need to support SRS transmission for VoIP UEswithout introducing large respective overhead in the UL of thecommunication system. Moreover, there is a need for the SRS transmissionfrom VoIP UEs to enable optimum sounding conditions in order for theNode B to perform link adaptation. Link adaptation may be in the form ofTPC commands or MCS adjustments transmitted by the serving Node B to aVoIP UE.

Additionally, considering the voice activity, it is desirable tore-assign radio resources in the silent period, i.e., when a VoIP UEdoes not have a data packet to transmit, to another UE in order toimprove BW utilization. A VoIP UE may transmit a Release Request (RR) toits serving Node B to indicate that its buffer is empty. Conversely,when a VoIP UE exits a silent period, it needs to send a Service Request(SR) to indicate that it has packets for transmission. This operation isillustrated in FIG. 11 for the case of RR but the same concept appliesin case of SR.

Referring to FIG. 11, a VoIP UE transmits packets 1110 and when itsbuffer empties, the VoIP UE sends a RR 1120. When the serving Node Breceives the RR 1130, it re-assigns the BW resources to the VoIPtransmission from another UE 1140.

The nature of the single-state transmission information the VoIP UEsends (RR, SR, etc.) is immaterial to the purposes of the presentinvention. The focus is instead on the signaling used by the VoIP UE tosend this single-state information.

The prior art considers that either a separate channel is used for thetransmission of the RR or SR, or a few bits are punctured from the CQIfeedback the VoIP UE sends to its serving Node B regarding the DL SNRoperating conditions and replaced with the transmission of the RR or SR.The first prior art option introduces additional UL overhead and systemcomplexity as a new channel needs to be defined and supported. Thesecond prior art option typically compromises the accuracy of the CQIreception and of the RR or SR reception, and increases the complexity ofthe Node B receiver.

There is consequently a need to provide a signaling mechanism for VoIPUEs to transmit state transition information, such as a RR or SR,without introducing additional overhead or compromising the quality ofother signals such as the CQI, while introducing only minimal additionalcomplexity to the Node B receiver operation.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve theaforementioned problems occurring in the prior art, and the presentinvention provides an apparatus and method for multiplexing thetransmission of at least one reference signal from a User Equipment (UE)not having any other signal transmission, i.e., no transmission of dataor control signals, with the transmission of a reference signal from atleast another UE that also transmits a data signal or a control signalduring the same transmission time interval.

Additionally, the present invention enables the sounding of theoperating bandwidth by a UE, to enable the serving Base Station (or NodeB) to perform link adaptation for the signal transmitted by the UE,without consuming additional bandwidth resources in the UpLink (UL) ofthe communication system.

Additionally, the present invention enables a UE to transmit stateinformation, such as a release request or a service request, to itsserving Node B by multiplexing the respective signal transmission withthe transmission of signals of the same structure transmitted from otherUEs, without consuming additional bandwidth resources in the UL of thecommunication system.

In accordance with an aspect of the present invention, a method fortransmitting a Reference Signal (RS) by a User Equipment (UE) in awireless communication system is provided. The method includestransmitting a DeModulation Reference Signal (DM RS) and informationdata in a sub-frame; and transmitting a Sounding Reference Signal (SRS)in a last symbol in another sub-frame. The DM RS is transmitted in amiddle symbol in each slot of the sub-frame, and the information data istransmitted in other symbols in each slot of the sub-frame.

In accordance with another aspect of the present invention, a method forreceiving a Reference Signal (RS) by a Node B in a wirelesscommunication system is provided. The method includes receiving aDeModulation Reference Signal (DM RS) and information data in asub-frame; and receiving a Sounding Reference Signal (SRS) in a lastsymbol in another sub-frame. The DM RS is received in a middle symbol ineach slot of the sub-frame, and the information data is received inother symbols in each slot of the sub-frame.

In accordance with another aspect of the present invention, a UE isprovided for transmitting a Reference Signal (RS) in a wirelesscommunication system. The UE includes a controller; and a transmitterfor transmitting a DeModulation Reference Signal (DM RS) and informationdata in a sub-frame, and for transmitting a Sounding Reference Signal(SRS) in a last symbol in another sub-frame. The DM RS is transmitted ina middle symbol in each slot of the sub-frame, and the information datais transmitted in other symbols in each slot of the sub-frame.

In accordance with another aspect of the present invention, a Node B isprovided for receiving a Reference Signal (RS) in a wirelesscommunication system. The Node B includes a controller; and a receiverfor receiving a DeModulation Reference Signal (DM RS) and informationdata in a sub-frame, and for receiving a Sounding Reference Signal (SRS)in a last symbol in another sub-frame. The DM RS is received in a middlesymbol in each slot of the sub-frame, and the information data isreceived in other symbols in each slot of the sub-frame.

In accordance with another aspect of the present invention, a method fortransmitting a Reference Signal (RS) by a User Equipment (UE) in awireless communication system is provided. The method includestransmitting a DeModulation Reference Signal (DM RS), information data,and a Sounding Reference Signal (SRS) in a sub-frame including twoslots, each of the two slot including seven symbols. The DM RS istransmitted in a middle symbol in each of the two slots, the SRS istransmitted in a last symbol in the sub-frame, and the information datais transmitted in first, second, third, fifth, sixth, and seventhsymbols in a first slot of the two slots, and in first, second, third,fifth, and sixth symbols in a second slot of the two slots.

In accordance with another aspect of the present invention, a method forreceiving a Reference Signal (RS) by a Node B in a wirelesscommunication system is provided. The method includes receiving aDeModulation Reference Signal (DM RS), information data, and a SoundingReference Signal (SRS) in a sub-frame including two slots, each of thetwo slots including seven symbols. The DM RS is received in a middlesymbol in each of the two slots, the SRS is received in a last symbolthe sub-frame, and the information data is transmitted in first, second,third, fifth, sixth, and seventh symbols in a first slot of the twoslots, and in first, second, third, fifth, and sixth symbols in a secondslot of the two slots.

In accordance with another aspect of the present invention, a UE isprovided for transmitting a Reference Signal (RS) in a wirelesscommunication system. The UE includes a controller; and a transmitterfor transmitting a DeModulation Reference Signal (DM RS), an informationdata, and a Sounding Reference Signal (SRS) in a sub-frame including twoslots, each of the two slots including seven symbols. The DM RS istransmitted in a middle symbol in each of the two slots, the SRS istransmitted in a last symbol in the sub-frame, and the information datais transmitted in first, second, third, fifth, sixth, and seventhsymbols in a first slot of the two slots, and in first, second, third,fifth, and sixth symbols in a second slot of the two slots.

In accordance with another aspect of the present invention, a Node B isprovided for receiving a Reference Signal (RS) in a wirelesscommunication system. The Node B includes a controller; and a receiverfor receiving a DeModulation Reference Signal (DM RS), information data,and a Sounding Reference Signal (SRS) in a sub-frame including twoslots, each of the two slots including seven symbols. The DM RS isreceived in a middle symbol in each slot of the two slots, the SRS isreceived in a last symbol in the sub-frame, and the information data istransmitted in first, second, third, fifth, sixth, and seventh symbolsin a first slot of the two slots, and in first, second, third, fifth,and sixth symbols in a second slot of the two slots.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an exemplary sub-frame structure for anSC-FDMA communication system;

FIG. 2 is a diagram illustrating multiplexing, in time and frequency,PUSCH transmissions from different UEs and SRS transmissions;

FIG. 3 is a block diagram illustrating an exemplary SC-FDMA transmitterfor transmitting data information;

FIG. 4 is a block diagram illustrating a first exemplary SC-FDMAtransmitter for transmitting a reference signal, an ACK/NACK signal, ora CQI signal, using a CAZAC-based sequence in the time domain;

FIG. 5 is a block diagram illustrating a second exemplary SC-FDMAtransmitter for transmitting a reference signal, an ACK/NACK signal, ora CQI signal, using a CAZAC-based sequence in the frequency domain;

FIG. 6 is a block diagram illustrating a first exemplary SC-FDMAreceiver for receiving a reference signal, an ACK/NACK signal, or a CQIsignal, using a CAZAC-based sequence in the time domain;

FIG. 7 is a block diagram illustrating a second exemplary SC-FDMAreceiver for receiving a reference signal, an ACK/NACK signal, or a CQIsignal, using a CAZAC-based sequence in the frequency domain;

FIG. 8 is a block diagram illustrating an exemplary construction oforthogonal CAZAC-based sequences through the application of differentcyclic shifts on a root CAZAC-based sequence;

FIG. 9 is a diagram illustrating an exemplary PUCCH structure fortransmitting ACK/NACK signals;

FIG. 10 is a diagram illustrating an exemplary PUCCH structure fortransmitting CQI signals;

FIG. 11 is a diagram illustrating an exemplary mechanism to releaseresources used for signal transmission by a UE;

FIG. 12 is a diagram illustrating multiplexing a reference signal from aUE having another signal transmission in the corresponding transmissiontime interval and a reference signal from a UE without any other signaltransmission in the corresponding transmission time interval; and

FIG. 13 is a diagram illustrating a link adaptation process for thesignal transmitted by a UE.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will be described morefully hereinafter with reference to the accompanying drawings. Thepresent invention may, however, be embodied in many different forms andshould not be construed as being limited to the embodiments set forthherein. Rather, these illustrative embodiments are provided so that thisdisclosure will be thorough and complete and will fully convey the scopeof the invention to those skilled in the art.

Additionally, although the present invention is described with referenceto a Single-Carrier Frequency Division Multiple Access (SC-FDMA)communication system, it also applies to all FDM systems in general andto Orthogonal FDMA (OFDMA), OFDM, FDMA, Discrete Fourier Transform(DFT)-spread OFDM, DFT-spread OFDMA, Single-Carrier OFDMA (SC-OFDMA),and SC-OFDM in particular.

The embodiments of the present invention solve problems related to theneed for multiplexing the transmission of Sounding Reference Signals(SRSs) and state information signals, such as a Release Request (RR) ora Service Request (SR), without incurring additional bandwidth overheadin the UpLink (UL) of a communication system.

An often underutilized resource in SC-FDMA signaling is the cyclicshifts used to multiplex the DM RS in the PUSCH or all signals in thePUCCH. Especially for VoIP UEs, where spatial domain multiplexing isunlikely, only a few out of a maximum of usually 6-12 cyclic shifts areused. It is therefore possible to orthogonally multiplex, through theuse of different cyclic shifts of the CAZAC-based sequence, the DM RSfrom a first UE having PUSCH transmission over a TTI with an RS from asecond UE having no other signal transmission. The RS from the second UEmay serve as SRS. This is illustrated in FIG. 12.

Referring to FIG. 12, assuming the PUSCH sub-frame structure describedin FIG. 1, during symbol 1210 used for RS transmission in each slot, theDM RS 1220 from UE1 and the SRS 1230 from UE2 are multiplexed usingdifferent cyclic shifts of the same CAZAC-based sequence. As it will besubsequently discussed, the same principle also directly applies for thePUCCH.

The serving Node B can therefore configure a first UE to transmit atleast one RS having the same structure but different cyclic shift as theDM RS of another UE, without the first UE having any other (non-RS)signal transmission in the respective TTI. The RS can serve as an SRS toenable link adaptation for PUSCH or PUCCH transmission from the firstUE. This can be achieved by the Node B either signaling a TPC command orconfiguring the MCS used by the first UE for its subsequent data orcontrol transmissions. FIG. 13 illustrates this process.

Referring to FIG. 13, the sub-frame 1310, where the UE transmits itsSRS, may be a few sub-frames before the sub-frame 1340 of its PUSCH orPUCCH transmission, depending on the offset between DL and ULtransmissions, on the propagation delay, and on the time it takes forthe Node B to process the SRS 1320 and generate/transmit the linkadaptation signaling 1330.

The previously described at least one RS transmission from a UE withoutany other (non-RS) signal transmission in the respective TTI isconfigured by the Node B specifying each of the at least one RStransmission parameters of cyclic shift and transmission sub-frame.Additionally, the Node B may further specify the RBs where the SRStransmission occurs. The Node B may specify these parameters explicitlyor implicitly. In the latter case, the RBs may be determined by theassigned cyclic shift or vice versa. For example, if the RS transmissionfrom a UE is assigned a first cyclic shift value, the transmission is inthe same RBs as for its PUSCH or PUCCH transmission while if it isassigned a second cyclic shift value, the transmission is in otherpredetermined RBs relative to the ones for the PUSCH or PUCCHtransmission.

Multiplexing at least one RS from one or more UEs with the DM RS from aUE having PUSCH transmission or with the PUCCH transmission from a UEenables the multiplexed RS to serve as an SRS with optimal BWutilization (no additional overhead). The transmission timing of the SRScan be chosen so that it is most relevant for link adaptation. Moreover,as the SRS power is concentrated in a few RBs, it provides for optimalSNR estimation. Also, as RBs in both BW sides can be sounded (the RStransmission in the first slot is in different BW than the RStransmission in the second slot), broad knowledge of the channelexperienced by the UE can be obtained by the serving Node B. For the lowUE speeds, this SRS can also serve as DM RS for a subsequent PUSCHtransmission, effectively doubling the DM RS power, improving thechannel estimation, and providing substantial performance gainsparticularly at low operating SINRs.

When there are only a few UEs in the system, the transmission of atleast one RS from a UE without any other (non-RS) signal transmission inthe respective TTI can still follow the same principles, but instead ofbeing multiplexed with the PUSCH DM RS from another UE, it may insteadbe multiplexed in an RB allocated to PUCCH. As for the PUSCH DM RStransmission, the PUCCH transmission is also assumed to be throughCAZAC-based sequences and the multiplexing of UEs is performed usingdifferent cyclic shifts of the CAZAC-based sequence as it was previouslydescribed.

If the RS multiplexing from a first UE is with the ACK/NACK transmissionfrom another UE, the Node B informs the first UE of the respective RBand of the corresponding multiplexing rules it needs to apply includingthe appropriate orthogonal cover in each slot and the appropriate cyclicshift in each SC-FDMA symbol. The same principle as described in FIG. 11applies, but instead of a single DM RS per slot, the multiplexingapplies over the entire slot because it consists of transmission ofCAZAC-based sequence as illustrated in FIG. 9.

The same principle also applies if the RS multiplexing from a first UEis with the CQI transmission from another UE, which is also through thetransmission of CAZAC-based sequences, as illustrated in FIG. 10. Themultiplexing of RS from a first UE with the RS and CQI signals fromanother UE is again through different cyclic shifts of a CAZAC-basedsequence.

If no cyclic shifts are available in the PUCCH (for example, in theACK/NACK or CQI transmission), some RBs in some sub-frames may bereserved for RS transmission from a few UEs.

State transition information, such as a Release Request (RR) or aService Request (SR), can also be sent using RS transmission withdifferent cyclic shifts.

In a first embodiment, the present invention assumes that a UE isassigned at least two cyclic shift values. The first cyclic shift valuecan be used either for DM RS transmission in the PUSCH as illustrated inFIG. 1, or for PUCCH transmission as illustrated in FIG. 9 or FIG. 10.The second cyclic shift value is used for RS transmission without anyother (non-RS) signal transmission in the respective TTI either duringthe DM RS symbols in the PUSCH or throughout the PUCCH. This RS serveseither as an RR or as an SR and is multiplexed with the DM RS or thePUCCH transmission from another UE, which uses a third cyclic shiftvalue which may be the same as the first cyclic shift value.

A fourth cyclic shift value may be reserved to never be used, either forthe DM RS in the PUSCH or for the PUCCH, so that the serving Node B candetermine whether either a RR or a SR was transmitted. This can beachieved by comparing the output energy between the demodulation resultsusing the second and fourth cyclic shift values. As the fourth cyclicshift value is not used for any transmission, the respectivedemodulation result will contain only noise. If the RS indicating an RRor an SR is transmitted using the second cyclic shift, the demodulationresult will contain both the corresponding signal and noise. For thePUSCH, an exemplary demodulation process was described above in FIG. 6or FIG. 7. Practically the same process also applies for the PUCCH.

In a second embodiment, the present invention assumes that a UE isassigned at least three cyclic shift values. The first cyclic shiftvalue is used for the transmission of a DM RS in the PUSCH asillustrated in FIG. 1 or for PUCCH transmission as illustrated in FIG. 9or FIG. 10. The second and third cyclic shift values are used fortransmission of a RS without any other (non-RS) signal transmission inthe corresponding TTI to indicate, respectively, an RR and the oppositeof an RR (that is, that the UE still has data to transmit). The RS usingthe second or third cyclic shift value can be multiplexed with the DM RSof another UE having PUSCH transmission and using a fourth cyclic shiftvalue, which may be the same as the first cyclic shift value, or withthe PUCCH transmission of another UE using a fourth cyclic shift value.The Node B determines whether an RR or its opposite was sent bycorrelating the received signal during the RS symbols in the PUSCH orduring the entire PUCCH with the second and third cyclic shift valuesand choosing the one providing the larger output energy. For the PUSCH,an exemplary demodulation process was described above relating to FIG. 6or FIG. 7. The same process practically applies also for the PUCCH.

While the present invention has been shown and described with referenceto certain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention as defined by the appended claims.

What is claimed is:
 1. A method for transmitting a reference signal (RS)by a user equipment (UE) in a wireless communication system, the methodcomprising: transmitting a demodulation reference signal (DM RS) andinformation data in a sub-frame; and transmitting a sounding referencesignal (SRS) in a last symbol in a second slot from among two slotsincluded in another sub-frame, wherein the DM RS is transmitted in onlya middle symbol in each slot of the sub-frame, and wherein theinformation data is transmitted in other symbols in each slot of thesub-frame.
 2. The method of claim 1, wherein a cyclic shift value usedfor transmitting the DM RS is different from a cyclic shift value usedfor transmitting the SRS.
 3. The method of claim 1, wherein the DM RSand the information data are transmitted over a same bandwidth.
 4. Themethod of claim 1, wherein a bandwidth used for transmitting the DM RSis different from a bandwidth used for transmitting the SRS.
 5. A methodfor receiving a reference signal (RS) by a node B in a wirelesscommunication system, the method comprising: receiving a demodulationreference signal (DM RS) and information data in a sub-frame; andreceiving a sounding reference signal (SRS) in a last symbol in a secondslot from among two slots included in another sub-frame, wherein the DMRS is received in only a middle symbol in each slot of the sub-frame,and wherein the information data is received in other symbols in eachslot of the sub-frame.
 6. The method of claim 5, wherein a cyclic shiftvalue used for receiving the DM RS is different from a cyclic shiftvalue used for receiving the SRS.
 7. The method of claim 5, wherein theDM RS and the information data are received over a same bandwidth. 8.The method of claim 5, wherein a bandwidth used for receiving the DM RSis different from a bandwidth used for receiving the SRS.
 9. A userequipment (UE) for transmitting a reference signal (RS) in a wirelesscommunication system, the UE comprising: a controller; and a transmitterconfigured to transmit a demodulation reference signal (DM RS) andinformation data in a sub-frame, and to transmit a sounding referencesignal (SRS) in a last symbol in a second slot from among two slotsincluded in another sub-frame, wherein the DM RS is transmitted in onlya middle symbol in each slot of the sub-frame, and wherein theinformation data is transmitted in other symbols in each slot of thesub-frame.
 10. The UE of claim 9, wherein a cyclic shift value used fortransmitting the DM RS is different from a cyclic shift value used fortransmitting the SRS.
 11. The UE of claim 9, wherein the DM RS and theinformation data are transmitted over a same bandwidth.
 12. The UE ofclaim 9, wherein a bandwidth used for transmitting the DM RS isdifferent from a bandwidth used for transmitting the SRS.
 13. A node Bfor receiving a reference signal (RS) in a wireless communicationsystem, the node B comprising: a controller; and a receiver configuredto receive a demodulation reference signal (DM RS) and information datain a sub-frame, and to receive a sounding reference signal (SRS) in alast symbol in a second slot from among two slots included in anothersub-frame, wherein the DM RS is received in only a middle symbol in eachslot of the sub-frame, and wherein the information data is received inother symbols in each slot of the sub-frame.
 14. The node B of claim 13,wherein a cyclic shift value used for receiving the DM RS is differentfrom a cyclic shift value used for receiving the SRS.
 15. The node B ofclaim 13, wherein the DM RS and the information data are received over asame bandwidth.
 16. The node B of claim 13, wherein a bandwidth used forreceiving the DM RS is different from a bandwidth used for receiving theSRS.
 17. A method for transmitting a reference signal (RS) by a userequipment (UE) in a wireless communication system, the methodcomprising: transmitting a demodulation reference signal (DM RS),information data, and a sounding reference signal (SRS) in a sub-frameincluding two slots, each of the two slot including seven symbols,wherein the DM RS is transmitted in a middle symbol in each of the twoslots, wherein the SRS is transmitted in a last symbol in a second slotfrom among the two slots, and wherein the information data istransmitted in first, second, third, fifth, sixth, and seventh symbolsin a first slot from among the two slots, and in first, second, third,fifth, and sixth symbols in the second slot.
 18. The method of claim 17,wherein a cyclic shift value used for transmitting the DM RS isdifferent from a cyclic shift value used for transmitting the SRS. 19.The method of claim 17, wherein the DM RS and the information data aretransmitted over a same bandwidth.
 20. The method of claim 17, wherein abandwidth used for transmitting the DM RS is different from a bandwidthused for transmitting the SRS.
 21. A method for receiving a referencesignal (RS) by a node B in a wireless communication system, the methodcomprising: receiving a demodulation reference signal (DM RS),information data, and a sounding reference signal (SRS) in a sub-frameincluding two slots, each of the two slots including seven symbols,wherein the DM RS is received in a middle symbol in each of the twoslots, wherein the SRS is received in a last symbol in a second slotfrom among the two slots, and wherein the information data is receivedin first, second, third, fifth, sixth, and seventh symbols in a firstslot from among the two slots, and in first, second, third, fifth, andsixth symbols in the second slot.
 22. The method of claim 21, wherein acyclic shift value used for receiving the DM RS is different from acyclic shift values used for receiving the SRS.
 23. The method of claim21, wherein the DM RS and the information data are received over a samebandwidth.
 24. The method of claim 21, wherein a bandwidth used forreceiving the DM RS is different from a bandwidth used for receiving theSRS.
 25. A user equipment (UE) for transmitting a reference signal (RS)in a wireless communication system, the UE comprising: a controller; anda transmitter configured to transmit a demodulation reference signal (DMRS), an information data, and a sounding reference signal (SRS) in asub-frame including two slots, each of the two slots including sevensymbols, wherein the DM RS is transmitted in a middle symbol in each ofthe two slots, wherein the SRS is transmitted in a last symbol in asecond slot from among the two slots, and wherein the information datais transmitted in first, second, third, fifth, sixth, and seventhsymbols in a first slot from among the two slots, and in first, second,third, fifth, and sixth symbols in the second slot.
 26. The UE of claim25, wherein a cyclic shift value used for transmitting the DM RS isdifferent from a cyclic shift value used for transmitting the SRS. 27.The UE of claim 25, wherein the DM RS and the information data aretransmitted over a same bandwidth.
 28. The UE of claim 25, wherein abandwidth used for transmitting DM RS is different from a bandwidth usedfor transmitting the SRS.
 29. A node B for receiving a reference signal(RS) in a wireless communication system, the node B comprising: acontroller; and a receiver configured to receive a demodulationreference signal (DM RS), information data, and a sounding referencesignal (SRS) in a sub-frame including two slots, each of the two slotsincluding seven symbols, wherein the DM RS is received in a middlesymbol in each slot of the two slots, wherein the SRS is received in alast symbol in a second slot from among the two slots, and wherein theinformation data is received in first, second, third, fifth, sixth, andseventh symbols in a first slot from among the two slots, and in first,second, third, fifth, and sixth symbols in the second slot.
 30. The nodeB of claim 29, wherein a cyclic shift value used for receiving the DM RSis different from a cyclic shift values used for receiving the SRS. 31.The node B of claim 29, wherein the DM RS and the information data arereceived over a same bandwidth.
 32. The node B of claim 29, wherein abandwidth used for receiving DM RS is different from a bandwidth usedfor receiving the SRS.